The conversion of endogenous synthase D into I has been shown to be slow in several tissues from fasted and diabetic animals. Indirect evidence indicates that this may be due to the presence of highly phosphorylated forms of synthase, which are poor substrates for phosphoprotein phosphatase. We have recently observed that highly phosphorylated forms of purified synthase are poor substrates for purified phosphatase. It is therefore proposed to investigate whether the slow rate of D to I conversion in diabetic tissue extracts is due to (a) lower or inhibited phosphoprotein phosphatase activity, (b) the presence of highly phosphorylated forms of synthase, or (c) both. Glycogen synthase will be purified from skeletal muscle of normal and diabetic rabbits under conditions where phosphatases and kinases are inhibited. The synthases from these two sources will be characterized in terms of their alkali-labile phosphate content and other properties. These results will be used to prepare purified 32P-synthases with a phosphate content similar to that found in the normal and diabetic tissues. These 32P-synthase preparations will be used to investigate phosphoprotein phosphatase activities in skeletal muscle extracts from normal and diabetic rabbits. In addition, the levels of phosphoprotein phosphatase inhibitors will also be studied in skeletal muscle extracts. The investigation will give insight into the regulation of glycogen synthase and phosphoprotein phosphatase activities.